The present invention relates to an apparatus and method for de-prioritizing bypass packets in a frame relay system and, more particularly, effecting a prioritization scheme in a transcoder where access to a packet based network by mobile-to-mobile calls is given lower priority than calls between mobile users and landline users.
In the area of cellular telephony, a plurality of base stations each serving mobile wireless telephone users are connected together via an infrastructure that routes calls from a base station to another base station and also to existing landline based public switch telephone networks (PSTN's). Although various methods of communicating signals from base sites to their serving base stations exist, increasingly in wireless infrastructure systems packet based networks, such as frame relay, have been adopted to handle voice traffic as frame relay affords efficient use of bandwidth and lower cost as opposed to traditional voice or circuit switching networks.
Because frame relay was originally designed to handle bursty traffic data, packet switching networks such as frame relay are inherently less efficient than circuit switching networks in dealing with voice traffic, which tends to be periodic and less random. In order to achieve good voice quality, the delay of voice packets across the frame relay network must be minimal. Hence, when multiple users are vying for access to a frame relay pipe that is configured for serial transmission, in particular, minimal delay of voice communication signals becomes critical.
Another concern about voice traffic is that for mobile-to-landline calls, encoded wireless communication signals from a mobile station to a base station must be decoded by a voice processor in a transcoder (i.e., a device performing both encoding and decoding) at the base site before the voice information is sent to a PSTN. This step of decoding the signal from the wireless user presents additional delay to the voice traffic signals. In order to mitigate this delay, as well as prevent audio degradation due to double transcoding, wireless systems typically employ a bypass scheme that allows voice information sent from one mobile station to another mobile station to “bypass” the decoding and encoding steps performed in the transcoders of the base sites, thereby eliminating the delay inherent with these steps.
As mentioned above, voice processors in a base site must still vie for access to the frame relay pipe. Typically a control processor, which controls access of the voice processors to the serial frame relay pipe, allows frame relay access to the voice processors one at a time based on the order they come in. This is typically referred to as a FIFO (first in, first out) queue.
Thus, in a typical transcoder pool comprised of one control processor and 12 voice processors, for example, a packet transmission could be delayed by 11×(packet transmission time) milliseconds if all 12 voice processors have packets to send on the frame relay pipe at roughly the same time in a worst case scenario. Accordingly, no discrimination is made between bypass mode calls and normal mode calls (e.g., mobile-to-landline or vice versa) and, thus, normal calls requiring extra processing time for vocoding may be placed at the end of the FIFO queue and be transmitted after bypass calls requiring no decoding or encoding.